The US powered unchallenged to Olympic gold in the women's 4x400 metres relay on Saturday.
The quartet of DeeDee Trotter, Allyson Felix, Francena McCorory and Sanya Richards-Ross crossed the line in three minutes, 16.87 seconds.
Russia's foursome of Tatyana Ledovskaya, Olga
Nazarova, Maria Kulchunova and Olga Bryzgina claimed silver almost four seconds back.
Jamaica took bronze as Novlene Williams-Mills, Shericka Williams, Rosemarie Whyte and Christine Day clocked 3:20.95.